Fermi-level tuning in topological insulator (Bi_1-<i>x</i>Sb<i>_x</i>)₂Se₃thin films

Fermi-level (E_F) tuning is an indispensable technique for detection of Dirac features in 3D topological insulators (TIs). The alloy system of (Bi_1-xSb_x)₂Te₃ [1] has been a playground to observe quantum transport phenomena at the Dirac surface states owing to good E_F controllability with the Sb content. In this study, we report a successful E_F tuning in another prototypical 3D TI, (Bi_1-xSb_x)₂Se₃(BSS), thin films with Bi/Sb composition ratio in molecular-beam epitaxy growth and electric field effect. So far, the different crystal structures between rhombohedral Bi₂Se₃ and orthorhombic Sb₂Se₃ have limited thin films research based on BSS due to the low solubility limit of Sb into Bi₂Se₃ below x ~ 0.5. By insertion of Bi₂Se₃ buffer layer, the limit can be expanded to x ~ 0.8 [2]. Angle-resolved photoemission spectroscopy revealed Dirac surface states even at x ~ 0.7. We demonstrated ambipolar operation in the top-gate-type field-effect transistors based on the BSS film with x ~ 0.7, indicating electrical tuning of E_F across the Dirac point [3]. Our results will make a step forward to detailed investigation on the Dirac surface states in BSS-based heterostructures. [1] J. Zhang et al., Nat. Comm. 2, 574 (2011). [2] Y. Satake et al., submitted. [3] Y. Satake et al., in preparation.